Immune Decisions

Immune system cells flock to the site of an infection once residents there cry out for relief. The herding causes inflammation: swelling, redness, and pain. Then the immunizers collectively decide what to do.

“When it comes to immune responses, it’s the difference between life and death,” American biochemist Joshua Leonard explains. “If your body over-responds to a bacterial infection, then you could die from septic shock. If your body doesn’t respond enough, then you could die from rampant infection. Staying healthy requires the body to strike a balance between these extremes.”

The immune system is decentralized. Each immune cell has its own mind. But cells innately know they need to work together.

“Cells observe their surroundings to get a sense of their neighbors,” says American biochemist Joseph Muldoon. “Each cell becomes poised to respond.”

But before acting out, immune cells collectively decide who is going to do what. “The cells make a coordinated decision. They don’t uniformly activate but instead collectively decide how many cells will activate, so that together, the system can fend off a threat without dangerously overreacting,” explains American biochemist Joshua Leonard. “The population response is calibrated,” concurs Muldoon.

Collective decision-making among cells is archaic. Bacteria often coordinate their activities to feed or defend themselves. Biofilms are cities of bacteria which behave more civilly and more readily coordinate than people do.

“In responding to external cues, cells are faced with many options, but by sharing information a population of cells can make more effective decisions than can each individual alone,” marvels Muldoon.


Ishi Nobu, The Web of Life, BookBaby (2019).

Joseph J. Muldoon et al, “Macrophages employ quorum licensing to regulate collective activation,Nature Communications (13 February 2020).

Immune cells congregate and coordinate with neighbors to decide whether to react,” Sci News (13 February 2020).